This invention relates generally as indicated to an aircraft drainmast assembly and, more particularly, to a drainmast assembly including a lightning protection grounding plate which may be installed from outside the aircraft.
A drainmast is used to eject waste water from an aircraft during flight and/or when the aircraft is on the ground. Waste water may be generated from many sources, such as the aircraft galley wherein water, soft drinks, coffee, wine, orange juice and other potable liquids are collected. Waste water can also accumulate from engine and other air inlets that trap water from condensation or ingest rain. In any event, the drainmast assembly communicates with the outlet of the aircraft""s waste water system.
A drainmast typically comprises a fairing, a drain tube, and some type of heater. With particular reference to a rear discharge drainmast, the fairing will commonly include a mounting flange, a mast, and an exit cap. The mast extends from the flange to the exit cap and is shaped to be aerodynamically advantageous. The drain tube is usually made of a metallic material and is positioned within the fairing cavity. The inlet of the drain tube is coupled to an adapter which is connected to the outlet of the aircraft waste water system. The outlet of the drain tube is positioned at the exit of the fairing cap. The heater is provided to prevent freezing of the waste water as it passes through the drain tube.
Lightning strikes involving aircraft are a common occurrence. If a lightning strike was to occur near a drainmast, it is expected to attach to the distal end of the fairing exit cap. The high currents created by the strike are expected to travel up the metallic drain tube in search for ground. If the current is not quickly transferred to an electrical ground, it could continue to travel along the adjacent drain tube and penetrate further into the aircraft.
Grounding may be accomplished by using a jumper wire, supplied with a ring terminal, that is suitable for attachment to the airframe which typically represents electrical ground for the aircraft. When using a jumper wire, care must be taken to ensure the wire is of sufficient length to allow easy installation, but short enough so as to not create any sharp bends after installation. Any bends in the wire become likely break points if the wire has to carry major portions of the lightning current. Induced voltage on long jumper wires may also prove to be sufficient to spark over a direct, shorter path across an air gap in search of ground. Furthermore, there must be a suitable airframe attachment point for the ring terminal used on the jumper wire. This attachment point must be cleaned and alodined prior to installation of the ring terminal, to ensure good metal-to-metal contact, without metal corrosion. This can present a problem to aircraft maintenance workers, as it is not always easy to find, clean and alodine a suitable grounding point.
The present invention provides a drainmast assembly incorporating a grounding plate for lightning protection purposes. The design of the drainmast assembly is such that the grounding plate may be installed from outside the aircraft and, in any event, eliminates the need for a maintenance worker to clean and alodine an attachment point within the aircraft.
More particularly, the present invention provides a drainmast assembly comprising a drainmast for ejection of waste water from an aircraft and a grounding plate for protection against lightning strike currents. The fairing is made of an electrically non-conductive material and includes a mounting flange, an exit cap, and an aerodynamically advantageously shaped mast extending from the mounting flange to the exit cap. The drain tube is made of an electrically conductive material (e.g., metal), is positioned at least partially within the fairing, and includes an inlet which communicates with an aircraft waste water system and an outlet positioned within the fairing""s exit cap.
The grounding plate is made of an electrically conductive material and is attached to the drain tube in such manner (e.g., welding) that an electrically conductive path is established between the grounding plate and the drain tube. The grounding plate is placed in contact with the aircraft fuselage during installation of the drainmast. As a result, lightning strike currents will travel from the drain tube to the grounding plate to the aircraft fuselage. The grounding plate will have a higher current carrying capacity than, for example, a jumper wire, due to it""s substantially larger cross-sectional area.
The grounding plate may be pressed against the outside surface of the fuselage by an elastomeric gasket installed between the composite fairing and grounding plate. When the drainmast assembly is installed, sufficient pressure is developed between the fairing mounting flange and fuselage attachment points to ensure good metal-to-metal contact between the grounding plate and fuselage. This allows for a simple lightning protection installation from the outside of the aircraft. It is not necessary to remove paint or apply any protective coatings to the surface of the fuselage, as any paint in the bonding region will most likely be burned away if a strike were to occur.
To prevent the lightning current from traveling further into the aircraft, an adapter made from electrically non-conductive material may be used to couple the inlet of the drain tube to the outlet of the air waste water system. In this manner, the lightning current will be prevented from sparking from the drain tube to the aircraft waste water system outlet pipe.
These and other features of the invention are fully described and particularly pointed out in the claims. The following descriptive annexed drawings set forth in detail certain illustrative embodiments of the invention, these embodiments being indicative of but a few of the various ways in which the principles of the invention may be employed.